Electro-optic modulator

ABSTRACT

An electro-optical modulator device includes an optical signal path partially defined by a waveguide portion, a radio frequency (RF) signal path partially defined by a conductive line portion, an interaction region where an RF signal propagating in the RF signal path interacts with an optical signal propagating in the optical signal path to modulate the optical signal, and a first tuning portion arranged proximate to the conductive line portion, the first tuning portion including a conductive portion and a switch portion operative to connect the conductive portion to ground.

FIELD OF INVENTION

The present invention relates generally to electro-optic devices andmethods, and more specifically, to electro-optic modulators.

DESCRIPTION OF RELATED ART

Electro-optic modulators include an arrangement of optical wave guideportions and conductive line portions. The optical wave guide portionsare operative to facilitate the propagation of optical signals and theconductive line portions propagate input radio frequency (RF) signals.The RF signals facilitate an electro-optic effect that changes therefractive index of the waveguide materials when the RF signals interactwith the waveguide material. The arrangement provides an interactionbetween the optical signals and the RF signals such that the opticalsignals may be modulated by the input RF signals.

BRIEF SUMMARY

According to one embodiment of the present invention, an electro-opticalmodulator device includes an optical signal path partially defined by awaveguide portion, a radio frequency (RF) signal path partially definedby a conductive line portion, an interaction region where an RF signalpropagating in the RF signal path interacts with an optical signalpropagating in the optical signal path to modulate the optical signal,and a first tuning portion arranged proximate to the conductive lineportion, the first tuning portion including a conductive portion and aswitch portion operative to connect the conductive portion to ground.

According to another embodiment of the present invention, anelectro-optical modulator device system includes an optical signal pathpartially defined by a waveguide portion, a radio frequency (RF) signalpath partially defined by a conductive line portion, an interactionregion where an RF signal propagating in the RF signal path interactswith an optical signal propagating in the optical signal path tomodulate the optical signal, a first tuning portion arranged proximateto the conductive line portion, the first tuning portion including aconductive portion and a switch portion operative to connect theconductive portion to ground, and a controller portion communicativelyconnected to the switch portion of the first tuning portion, thecontroller portion operative to control a state of the switch portion.

According to yet another embodiment of the present invention, anelectro-optical modulator device includes a substrate, a radio frequency(RF) signal path partially defined by a conductive line portion arrangedon the substrate, an optical signal path partially defined by awaveguide portion arranged on the substrate, an interaction region wherean RF signal propagating in the RF signal path interacts with an opticalsignal propagating in the optical signal path to modulate the opticalsignal, and a first tuning portion arranged on the substrate proximateto the conductive line portion, the first tuning portion including aconductive portion and a switch portion operative to connect theconductive portion to ground.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates a top view of a portion of an exemplary embodiment ofan electro-optical modulator device.

FIG. 2 illustrates a top view of an exemplary arrangement of aconductive line and tuning portion.

FIG. 3 illustrates a side partially cut-away view of an exemplaryembodiment of a tuning portion.

FIG. 4 illustrates a top view of a portion of another exemplaryembodiment of an electro-optical modulator device.

FIG. 5 illustrates a portion of an exemplary embodiment of the device inthe region 5 (of FIG. 4).

FIG. 6 illustrates another alternate exemplary embodiment of the devicein the region 5 (of FIG. 4).

FIG. 7 illustrates a block diagram of an exemplary method for operatingthe electro-optical devices.

DETAILED DESCRIPTION

Previous electro-optic modulators included a waveguide portion thatpropagated optical signals and a conductive line portion that propagatedradio frequency (RF) signals. The interaction of the RF signals with theoptical signals was operative to modulate the optical signals. Thoughdevices tend to be designed such that the optical signals and the RFsignals generally propagate at similar speeds, the materials and thegeometry of the electro-optic modulators may affect the relativepropagation speeds of the optical signals and the RF signals. If, forexample, the propagation speed of the RF signals does not match thepropagation speed of the optical signals in the interactive regions ofthe electro-optical device, the bandwidth of the modulator may beundesirably reduced.

The illustrated exemplary embodiments described herein provide a methodand system for matching the propagation speeds of the RF signals withthe optical signals in the interaction regions of an electro-opticaldevice while the device is operating. Such matching (or tuning) of thespeeds of the signals may increase the effective bandwidth of theelectro-optical device and system.

FIG. 1 illustrates a top view of a portion of an exemplary embodiment ofan electro-optical modulator device 100. In this regard, the device 100is arranged on a substrate such as for example a silicon substratematerial. A waveguide portion 102 is arranged on the substrate.Conductive lines 104 are arranged on a layer over or next to thewaveguide portion 102. The waveguide portion 102 is operative topropagate a continuous wave (CW) optical input signal, and theconductive lines 104 are operative to propagate RF input signals. Thewaveguide portion 102 and the conductive lines 104 overlap ininteraction regions 106. The interaction of the RF signal with thewaveguide portions 102 in the interaction regions 106 affects themodulation of the CW optical input light resulting in a modulated orencoded optical output signal. As discussed above, the geometry and thematerials of the device 100 may affect the propagation speed of theoptical and RF signals. In the illustrated exemplary embodiment, the RFsignal propagates at a higher speed than the optical signal. Thus,reducing the propagation speed of the RF signal will reduce the relativedifference in propagation speeds between the optical signal and the RFsignal.

The group velocity of the RF signal is a function of the lineinductance, and the capacitance of the conductive lines 104. Changingthe capacitance or inductance of the conductive lines 104 will changethe group velocity of the RF signal. The illustrated embodiment includesa plurality of tuning portions 108 that are arranged across or proximateto the conductive lines 104. The tuning portions 108 are electricallyinsulated from the conductive lines 104, and may be arranged forexample, on a layer of material on the substrate that is insulated fromthe conductive lines 104. Each tuning portion 108 is connected to groundvia one or more switch devices 110 that may be controlled by acontroller (described below). When the switch devices 110 are closed(i.e., the tuning portion 108 is connected to ground on either one end,opposing ends of the tuning portion 108, or a switch device 110 arrangedin the a medial region of the tuning portion 108) for a particulartuning portion 108, the capacitance of the associated conductive line104 is increased. The increase in the capacitance of the conductive line104 decreases the velocity of the RF signal propagating in theconductive line 104.

Though the illustrated embodiment includes two tuning portions 108arranged and associated with each conductive line 104, alternativeembodiments may include any number of tuning portions 108 per conductiveline 104. Each tuning portion 108 may be individually controlled suchthat the effective capacitance of the conductive line 104 may beincreased incrementally by affecting the switch device(s) 110 connectingparticular tuning portion 108 to ground. By changing the states of thetuning portion 108 (i.e., the states of the switch device 110 connectingthe tuning portion 108 to ground), the effective capacitance of theconductive lines 104 may be increased or decreased to affect thevelocity of the RF signal to approach or substantially match the speedof the optical signal.

FIG. 2 illustrates a top view of an exemplary arrangement of aconductive line 104 and tuning portion 108. The line loading elementsinclude a conductive portion 202 connected to the switch devices 110.Each of the conductive portions 202 may be selectively and individuallyconnected to ground by closing the switch device 110 on an end of thetuning portion 108. The switch devices 110 are controlled by acontroller portion 204, which is operative to output signals that changethe state of the switch devices 110. The controller portion 204 mayinclude, for example, a processor or a logic circuit operative toreceive inputs, and process the input and output signals. In theillustrated embodiment, the controller 204 may close the switch device110 a, which connects the conductive portion 202 a to ground. Such aconnection results in an increase in the capacitance of the conductiveline 104. As discussed above, the increase in the capacitance of theconductive line 104 decreases the velocity of the RF input signal(decreasing the relative difference between the speed of the RF inputand the optical signal (described above). If a further reduction of thevelocity of the RF input is desired, the controller may, for example,close the switch device 110 b to connect the conductive portion 202 b toground, thereby further increasing the capacitance of the conductiveline 104. The capacitance may be further increased, if desired, byclosing the switch device 110 of other tuning portions 108.

FIG. 3 illustrates a side partially cut-away view of an exemplaryembodiment of a tuning portion 108. The conductive portion 202 isconnected to the switch device 110. In the illustrated embodiment, theswitch device 110 includes one or more transistors. The switch device110 is connected to ground the node 302 and the controller 204. Thetuning portion 108 is arranged in an insulating layer 303, such as, forexample, an oxide or nitride material that is disposed on the substrate301. The conductive line 104 is arranged on the insulating layer 303.Though the illustrated embodiment includes a substrate 301 and aninsulating layer 303, the device may include any number of layersincluding any variety of materials. Though one switch device 110 isshown, alternate embodiments may include two or more switch devices 110such that each end of the conductive portion 202 is connected to groundvia a switch device 110, or alternate embodiments may include a switchdevice 110 in a medial region of the conductive portion 202 that resultsin a path to ground between ends of the conductive portion 202 when theswitch device 110 is closed.

FIG. 4 illustrates a top view of a portion of another exemplaryembodiment of an electro-optical modulator device 400. The device 400includes modulation paths 401 and 403. Each modulation path 401 and 403includes a conductive line 404 and a waveguide portion 402. Theconductive lines 404 are connected to push-pull RF inputs 406 andpush-pull RF outputs 408. The waveguide portions 402 are connected tooptical signal input portions 410 and optical signal output portions412. The optical signals are modulated by the RF signals in interactionor modulation regions 414. A plurality of tuning portions 108 arearranged over portions of the conductive lines 404. The tuning portions108 connected to ground regions 416 and are insulated from theconductive lines 404. The conductive lines 404 are isolated from theground regions 416 by insulator regions 418. The operation of the device400 is similar to the operation of the exemplary embodiments describedabove and is described in further detail in FIG. 5 below.

FIG. 5 illustrates a portion of an exemplary embodiment of the device400 in the region 5 (of FIG. 4). In this regard, the tuning portions 108a, 108 b, and 108 c are arranged in respective groups 501, 503, and 505each communicatively connected and controlled by the controller 214 suchthat the controller 214 may selectively change the states of theswitching devices 110 (of FIG. 2) for each of the plurality of tuningportions 108 a, 108 b, 108 c in each group 501, 503, and 505.

FIG. 6 illustrates another alternate exemplary embodiment of the device400 in the region 5 (of FIG. 4). In this regard, the tuning portions 108a, 108 b, 108 c, 108 d, 108 e, 108 f, 108 g, 108 h, and 108 i are eachcommunicatively connected and independently controlled by the controller214 such that the controller 214 may selectively change the states ofthe switching devices 110 (of FIG. 2) for each of the plurality oftuning portions 108 a, 108 b, 108 c, 108 d, 108 e, 108 f, 108 g, 108 h,and 108 i individually. Each of the controller portions 214 may beoperative to receive a signal indicative of a performance measurement(performance metric) of the device as shown in FIG. 7, such as, forexample, a measured bandwidth of the device 400 or a measurement of amodulation penalty of the device. The signal may be used in someembodiments to control the device 400 as described below. A modulationpenalty is defined for a specific modulation format. There are manytypes of modulation formats, for example, non-return to zero (NRZ),differential phase shift keying (DPSK) and multi-level coding (PAM4 orPAM8). For example, for NRZ the modulation penalty is defined asExtinction ratio converts to modulation penalty,PowerPenalty=10*Log[(ER−1)/(ER+1)], where ER is the extinction ratio,which is the ratio of the power in a ‘zero’ bit divided by the power ina ‘one’ bit.

FIG. 7 illustrates a block diagram of an exemplary method for operatingthe electro-optical devices described above. In this regard, in block702, the performance of the electro-optical device is measured. Once theperformance of the device is measured, the state of a tuning portion 108(of FIG. 1) is changed to connect the tuning portion 108 to ground bychanging the state of the switch devices 110 with, for example, thecontroller 214. In block 706, the performance of the electro-opticaldevice is measured. In block 708, if the performance of theelectro-optical device has increased (e.g., the first measured bandwidthin block 702 is compared with the second measured bandwidth of block 706to determine if the second measured bandwidth is greater than the firstmeasured bandwidth), the processes in blocks 704 and 706 may berepeated. In block 710, if the performance of the electro-optical devicehas not increased, whether the performance of the device has decreasedis determined. If yes, the state of a tuning portion 108 of the devicemay be changed to disconnect the tuning portion 108 from ground by, forexample, opening the switching devices 110 in block 712. The methoddescribed in FIG. 7 may be performed by, for example, the controller 214receiving an input indicative of the performance of the electro-opticdevice, or a technician who sends inputs to the controller 214 tocontrol the states of the tuning portions 108.

Alternately, a quality (or qualities) of a data transmission could bemonitored real-time and used as the input information for the controllerto appropriately modify which switches are turned on and how theelectro-optic modulator bandwidth should be configured. Furthermore, ifthe transmission system is a mesh network with optical add-drop modules,the quality of the existing data within the network may be monitored sothat the data added to the network can be made to have distortionsimilar to that travelling through the optical add-drop module.

Once the states of the tuning portions 108 have been set, the statesmay, in some exemplary embodiments, be dynamically changed while theelectro-optical device is modulating optical signals in normaloperation, or the states may be set or calibrated for a particular modeof operation.

Though the illustrated exemplary method of FIG. 7 includes increasingthe performance of the device by changing states of the tuning portions108, it may be desirable in some embodiments to reduce the performanceof the device (e.g., reduce the bandwidth of the device). In thisregard, a similar logical method is performed where the states of thetuning portions 108 are changed to reduce the performance of the deviceto a desired performance level.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the preferred embodiment to the invention had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

What is claimed is:
 1. An electro-optical modulator device comprising:an optical signal path partially defined by a waveguide portion; a radiofrequency (RF) signal path partially defined by a conductive lineportion; an interaction region where an RF signal propagating in the RFsignal path interacts with an optical signal propagating in the opticalsignal path to modulate the optical signal; and a first tuning portionarranged proximate to the conductive line portion, the first tuningportion including a conductive portion, a first switch portion and asecond switch portion, each of the first switch portion and the secondswitch portion connected to the conductive portion and ground.
 2. Thedevice of claim 1, wherein the conductive portion is disposed in anarrangement overlapping the conductive line portion.
 3. The device ofclaim 1, wherein the conductive portion of the first tuning portion iselectrically isolated from the conductive line portion.
 4. The device ofclaim 1, further comprising a second tuning portion, the second tuningportion including a conductive portion and a switch portion operative toconnect the conductive portion to ground.
 5. The device of claim 1,further comprising a controller portion communicatively connected to theswitch portion of the first tuning portion, the controller portionoperative to control a state of the switch portion.
 6. The device ofclaim 4, further comprising a controller portion communicativelyconnected to the switch portion of the first tuning portion and theswitch portion of the second tuning portion, the controller portionoperative to control a state of the switch portion of the first tuningportion and a state of the switch portion of the second tuning portion.7. An electro-optical modulator device system comprising: an opticalsignal path partially defined by a waveguide portion; a radio frequency(RF) signal path partially defined by a conductive line portion; aninteraction region where an RF signal propagating in the RF signal pathinteracts with an optical signal propagating in the optical signal pathto modulate the optical signal; a first tuning portion arrangedproximate to the conductive line portion, the first tuning portionincluding a conductive portion, a first switch portion and a secondswitch portion, each of the first switch portion and the second switchportion connected to the conductive portion and ground; and a controllerportion communicatively connected to the switch portion of the firsttuning portion, the controller portion operative to control a state ofthe switch portion.
 8. The system of claim 7, wherein the conductiveportion is disposed in an arrangement overlapping the conductive lineportion.
 9. The system of claim 7, wherein the conductive portion of thefirst tuning portion is electrically isolated from the conductive lineportion.
 10. The system of claim 7, further comprising a second tuningportion, the second tuning portion including a conductive portion and aswitch portion operative to connect the conductive portion to ground.11. The system of claim 10, wherein the controller portion iscommunicatively connected to the switch portion of the first tuningportion and the switch portion of the second tuning portion, thecontroller portion operative to control a state of the switch portion ofthe first tuning portion and a state of the switch portion of the secondtuning portion.
 12. An electro-optical modulator device comprising: asubstrate; a radio frequency (RF) signal path partially defined by aconductive line portion arranged on the substrate; an optical signalpath partially defined by a waveguide portion arranged on the substrate;an interaction region where an RF signal propagating in the RF signalpath interacts with an optical signal propagating in the optical signalpath to modulate the optical signal; and a first tuning portion arrangedon the substrate proximate to the conductive line portion, the firsttuning portion including a conductive portion, a first switch portionand a second switch portion, each of the first switch portion and thesecond switch portion connected to the conductive portion and ground.13. The device of claim 12, wherein the conductive portion is disposedin an arrangement overlapping the conductive line portion.
 14. Thedevice of claim 12, wherein the conductive portion of the first tuningportion is electrically isolated from the conductive line portion.